This invention relates to a mechanical pressing machine of the type in which a slider is reciprocally moved linearly relative to a frame through a crankshaft.
In a mechanical pressing machine employing a crankshaft, a connecting rod is connected at its one end to an eccentric portion of the continuously rotating crankshaft, and a slider is connected to the other end of the connecting rod, thereby converting a rotational motion of the crankshaft into a reciprocal linear motion of the slider. When imparting the reciprocal motion to the slider, an inertia load of the slider, an unbalanced load, a pressing load and so on give fluctuating load torques to the crankshaft through the connecting rod. When these fluctuating load torques increase, the crankshaft may fail to rotate only by a drive torque of a motor. To avoid this, a flywheel has heretofore been attached to one end of the crankshaft. An abruptly-fluctuating load torque of the crankshaft is absorbed by an inertia force of the flywheel, so that the maximum value of the input torque is alleviated. This enables the machine to be operated by an output torque of the relatively small motor.
Recently, because of an increasing demand for a small-size, high-density design of electronic components and also for a clean environment, it has been desired to provide a high-performance mechanical pressing machine less noisy and highly precise. Reviewing pressing machines from this point of view, it will be appreciated that the currently-available mechanical pressing machines are so designed as to absorb all of the fluctuating loads by means of a flywheel. It is very rational and most desirable from the viewpoint of a mechanism to absorb an excessively large load fluctuation, produced instantaneously as in a pressing operation, by the inertia force of a large flywheel; however, although a constant load fluctuation, produced when imparting a reciprocal motion to the slider, can be ignored during a low-speed operation, its energy exceeds the energy of the pressing operation during a high-speed operation, so that the speed of rotation of the crankshaft attached to the flywheel increases and decreases, and hence varies periodically for every revolution. It is known that such variations in rotation of the input drive system cause vibrations of the press and noises, and also adversely affect the durability of a clutch and a brake.